17/03/2020 update: thanks @indented-automation. Snippet to compare various filter options. Linked here: https://www.cookadam.co.uk/get-cmunusedsources

CompareFilteringOptions.ps1

$winFiles = Get-ChildItem c:\windows -Recurse -ErrorAction SilentlyContinue

$commands = @{
    'Where-Object' = {
        $exeFiles = $winFiles | Where-Object { $_.Extension -eq ".exe" }
    }
    'Where-Object (no script block)' = {
        $exeFiles = $winFiles | Where-Object Extension -eq ".exe"
    }
    '.Where' = {
        $exeFiles = $winFiles.Where{ $_.Extension -eq ".exe" }
    }
    'DataTable' = {
        $fileTable = New-Object System.Data.DataTable
        $fileTable.TableName = "AllMuhFiles"

        [void]$fileTable.Columns.Add("FileName")
        [void]$fileTable.Columns.Add("Parent")
        [void]$fileTable.Columns.Add("Extension")
        [void]$fileTable.Columns.Add("IsInf")

        ForEach($file in $winFiles) {
            [void]$fileTable.Rows.Add($file.Name, $file.Parent, $file.Extension)
        }

        $exeFiles = $fileTable.Select("Extension like '.exe'")
    }
    'foreach' = {
        $exefiles = foreach ($file in $winFiles) {
            if ($file.Extension -eq '.exe') {
                $file
            }
        }
    }
}

$commands.Keys | ForEach-Object {
    $testName = $_
    1..3 | ForEach-Object {
        [PSCustomObject]@{
            TestName  = $testName
            Attempt   = $_
            ElapsedMS = (Measure-Command -Expression $commands[$testName]).TotalMilliseconds
        }
    }
}